Facebook app bug. Help!!!


Hello guys. I owe a samsung galaxy s3 and since I have bought it i have had the same problem for 6 months. My facebook app or the facebook messenger app does not notificate me when a message has arrived but after some minutes. If i check the app it shows me the message but just doesn't notificate me. So when I'm in a chat with someone I have to check if the other person has messaged me otherwise the message will arrive some minutes after.

I don't know whats the problem but if you guys could help me it would be so awesome. Thanks.